<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .result {
            width: 300px;
            height: 200px;
            border: 1px solid red ;
        }
    </style>
</head>
<body>
    <button>点击发送请求</button>
    <div class="result"></div>
    <script>
        const btn = document.querySelector("button");
        const result = document.querySelector(".result");
        btn.addEventListener("click",function(){
            const xhr = new XMLHttpRequest();
            xhr.timeout = 2000;
            xhr.ontimeout = function() {
                alert("网络异常，请稍后重试！！");
            }
            xhr.onerror = function(){
                alert("你的网络似乎出了一些问题！")
            }
            xhr.open("GET",'http://127.0.0.1:8000/delay');
            xhr.send();
            xhr.onreadystatechange = function(){
               if (xhr.readyState === 4) {
                   if(xhr.status >= 200 && xhr.status <300) {
                      result.innerHTML = xhr.response();
                   }
               }
            }
        })
    </script>
</body>
</html>